Many vehicles today are equipped with a cruise control to make it easier for the driver to drive the vehicle. The desired speed can then be set by the driver, e.g. via a control device in the steering wheel console, and a cruise control system in the vehicle acts thereafter upon a control system so that it accelerates and brakes the vehicle in order to maintain a desired speed. If the vehicle is equipped with an automatic gear change system, the vehicle's gears are changed so that the vehicle can maintain the desired speed.
When a cruise control is used in hilly terrain, the cruise control system will try to maintain a set speed on upgrades. This results inter alia in the vehicle accelerating over the crest of a hill and possibly into a subsequent downgrade, making it necessary to brake to avoid exceeding the set speed, which is a fuel-expensive way of running the vehicle. it possible to save fuel.
By varying the vehicle's speed in hilly terrain it is possible to save fuel as compared with a conventional cruise control. This may be done in various ways, e.g. by calculations of the vehicle's current state (as with Scania Ecocruise®). If an upgrade is calculated, the system then accelerates the vehicle uphill. Towards the end of the climb, the system is programmed to avoid acceleration until the gradient has levelled out at the top, provided that the vehicle's speed does not drop below a certain level. By lowering the speed at the end of an upgrade, the vehicle can regain speed on a subsequent downgrade without using the engine to accelerate. When the vehicle approaches the bottom of a dip, the system endeavors to use kinetic energy to embark on the next upgrade at a higher speed than an ordinary cruise control. The system will easily provide acceleration at the end of the downgrade in order to maintain the vehicle's momentum. In undulating terrain, this means that the vehicle starts the next climb at a higher speed than normal. Avoiding unnecessary acceleration and using the vehicle's kinetic energy makes
If the topology ahead is made known by the vehicle having map data and GPS, such a system can be made more robust and can also change the vehicle's speed in anticipation.
A vehicle usually has a number of ECUs (electronic control units) which control various electronic systems in the vehicle. The engine in the vehicle is often controlled by an ECU of its own, called EMC (engine management system). A cruise control's logic may be situated in the EMS but this is sometimes not possible because the EMS has too little memory space and/or an already high processor load. Where the logic is in some other ECU than the EMS, desired speeds have to be sent via a Controller Area Network (CAN) to the regulator in the engine control system which is intended to regulate the vehicle's speed towards the desired speed.
A traditional Proportional/Integral/Derivative (PID) regulator regulates on a given speed reference value. Therefore, when this reference value is modified by the cruise control's logic and sent via a CAN, it is the PID regulator in the engine control system which is intended to regulate the vehicle speed, towards the given reference value. The cruise control predicts the vehicle's speed but there remains the problem of the cruise control logic trying to predict the speed while at the same time the engine control system tries to control the vehicle's speed. The regulator will control according to a gradually increasing error and will then not provide the engine with maximum torque at the beginning of an upgrade which has been incorporated in the speed prediction calculations.
Published patent application US 2005/0096183 refers to a speed regulator for a vehicle on a downgrade. Hills are here configured to have a particular gradient downhill, and when the driver switches on a gradient switch a constant speed for the vehicle is set for as long as the switch is on. A constant speed of the vehicle is thus set when the driver indicates that the vehicle is on a hill.
In U.S. Pat. No. 6,076,036 the cruise control is based on use of speed setting, the vehicle's current speed, acceleration and the change in the gradient of the road as measured by a sensor, to set the fuel flow for lower fuel consumption.
The object of the present invention is to propose improved cruise control of a vehicle when the vehicle's speed is to be predicted while at the same time being regulated, and in particular to avoid unnecessary fuel being injected into the engine because of an unstable control signal to the engine control system.